Every year, new model dirt bikes come with new innovative designs, more features inside and out, and a higher price tag. It’s common now-a-days for a new dirt bike to come with 2 or more different map settings with the ability to toggle between them easily via a switch mounted on the handlebars. That’s just one small example of how far dirt bikes have come. They seem to get lighter and faster almost every year now, which means a lot of time and money is going into engineering.

An OEM cast piston from a new model dirt bike.

However, the majority of these new-era dirt bikes come with cast pistons in the engine. Head and combustion chamber designs are evolving, creating more and more compression than was previously common, putting even more stress on the cast pistons. OEMs go with cast pistons to save on cost and production tooling, even though cast piston technology seems to fall behind the rest of the tech put into the bikes.

Alloy parts made via the casting process have a very random grain structure. Essentially, molten alloy is poured into a piston mold, then cooled, and voilà, you have a cast piston.

JE Pistons doesn’t feel the casting process is sufficient for the level of stress modern dirt bike engines put on pistons. JE has been offering high-performance forged pistons for late model 4-stroke dirt bikes since they broke into the professional racing scene in the late 90s and early 2000s.

Aluminum pucks cut to size and weight, ready to be forged into a piston.

Forging metal is a superior process to achieve strength for alloy parts. To create a forged piston, a billet aluminum puck is pressed with an incredible amount of pressure and heat onto a forging die, which contains the shape to be put into the soon-to-be piston. This process forces the molecular structure of the alloy to align and flow with the part, instead being random and creating weak spots in the piston.

JE has always tried to stay ahead of the curve, offering forged pistons for new model dirt bikes as soon as possible. Keeping with this trend, JE Pro Series pistons are now available for some of the most exciting new model dirt bikes. Pro Series pistons are now available for the 2017 and 2018 Honda CRF450R, 2017 KX250F, and the 2016 and 2017 Honda CRF250R.

Front to back: CRF450R, CRF250R, KX250F Pro Series pistons.

These Pro Series pistons are all Forged Side Relief designs, meaning piston skirt material is left where it is needed--on the intake and exhaust sides of the cylinder--but material is left off the non-critical areas. This design is a big weight saver over the traditional full-round design, and allows for better structural optimization.

JE Pro Series pistons for new model dirt bikes feature a Forged Side Relief Design.

Each of these pistons are equipped with accumulator grooves, which reduces pressure build up between the first and second rings, reducing ring flutter and creating a better ring seal.

The accumulator groove is below the top ring land, and reduces pressure build up.

Each Pro Series piston for these new models are available in the standard compression ratio, along with multiple high-compression options. They can be purchased in the following compression ratios: